The demand for sophisticated tools and approaches in heat management and control has triggered fast development of emerging fields including conductive thermal metamaterials, nanophononics, far-field and near-field radiative thermal management, etc. In this review, we cast a unified perspective on the control of heat transfer, based on which the related studies can be considered as complementary paradigms toward manipulating physical parameters and realizing unprecedented phenomena in heat transfer using artificial structures, such as thermal conductivity in heat conduction, thermal emissivity in radiation, and properties related to multi-physical effects. The review is divided into three parts that focus on the three main categories of heat flow control, respectively. Thermal conduction and radiation are emphasized in the first and second parts at both macro-and micro-scale. The third part discusses the efforts to actively introduce heat sources or tune the material parameters with multi-physical effects in both conduction and radiation, including works using thermal convection. We conclude the review with challenges in this research topic and new possibilities about topological thermal effects, heat waves, and quantum thermal effects.

Single-crystal metals have distinctive properties owing to the absence of grain boundaries and strong anisotropy. Commercial single-crystal metals are usually synthesized by bulk crystal growth or by deposition of thin films onto substrates, and they are expensive and small. We prepared extremely large single-crystal metal foils by “contact-free annealing” from commercial polycrystalline foils. The colossal grain growth (up to 32 square centimeters) is achieved by minimizing contact stresses, resulting in a preferred in-plane and out-of-plane crystal orientation, and is driven by surface energy minimization during the rotation of the crystal lattice followed by “consumption” of neighboring grains. Industrial-scale production of single-crystal metal foils is possible as a result of this discovery.

We study analytically and numerically the classical diffusive process which takes place in a chaotic billiard. This allows to estimate the conditions under which the statistical properties of eigenvalues and eigenfunctions can be described by Random Matrix Theory. In particular the phenomenon of quantum dynamical localization should be observable in real experiments.PACS numbers: 05.45.+b, 05.20.-y One of the main modifications that quantum mechanics introduces in our classical picture of deterministic chaos is "quantum dynamical localization" which results e.g. in the suppression of chaotic diffusive-like process which may take place in systems under external periodic perturbations. This phenomenon, first pointed out in the model of quantum kicked rotator [1], is now firmly established and observed in several laboratory experiments [2].For conservative Hamiltonian systems the question of localization is much less investigated. The situation here is much more intriguing : from one hand, in a conservative system, one may argue that there is always localization due to the finite number of unperturbed basis states effectively coupled by the perturbation; on the other hand a large amount of numerical evidence indicates that quantization of classically chaotic systems leads to results which appear in agreement with the predictions of Random Matrix Theory (RMT) [3].Recently the problem of localization in conservative systems has been explicitely investigated. In particular, on the base of Wigner band random matrix model, conditions for localization were explicitely given together with the relation between localization and level spacing distribution [4].Billiards are very important models in the study of conservative dynamical systems since they provide clear mathematical examples of classical chaos and their quantum properties have been extensively studied theoretically and experimentally. Moreover they are becoming increasingly relevant for the study of optical processes in microcavities which may lead to possible applications such as the design of novel microlasers or other optical devices [5].In this paper we focus our attention on a two dimensional chaotic billiard: the Bunimovich stadium, and study the classical diffusive process which takes place in angular momentum. This will allow us to predict the conditions for quantum localization and therefore the conditions under which the standard Random Matrix Theory is not applicable.We consider the motion of a particle having mass m, velocity v and elastically bouncing inside the stadium shown in Fig 1. We denote with R the radius of the semicircles and with 2a the length of the straight segments. The total energy is E = m v 2 /2.The statistical properties of the billiard are controlled by the dimensionless parameter ǫ = a/R and, for any ǫ > 0, the motion is ergodic, mixing and exponentially unstable with Lyapunov exponent Λ which, for small ǫ, is given by [6] Λ ∼ ǫ 1/2 .For the analysis of classical dynamics, a typical choice of canonical variables is (s, v t ) whe...

The process of oxidation of a copper surface coated by a layer of graphene in water-saturated air at 50 °C was studied where it was observed that oxidation started at the graphene edge and was complete after 24 h. Isotope labeling of the oxygen gas and water showed that the oxygen in the formed copper oxides originated from water and not from the oxygen in air for both Cu and graphene-coated Cu, and this has interesting potential implications for graphene as a protective coating for Cu in dry air conditions. We propose a reaction pathway where surface hydroxyl groups formed at graphene edges and defects induce the oxidation of Cu. DFT simulation shows that the binding energy between graphene and the oxidized Cu substrate is smaller than that for the bare Cu substrate, which facilitates delamination of the graphene. Using this process, dry transfer is demonstrated using poly­(bisphenol A carbonate) (PC) as the support layer. The high quality of the transferred graphene is demonstrated from Raman maps, XPS, STM, TEM, and sheet resistance measurements. The copper foil substrate was reused without substantial weight loss to grow graphene (up to 3 cycles) of equal quality to the first growth after each cycle. It was found that dry transfer yielded graphene with less Cu impurities as compared to methods using etching of the Cu substrate. Using PC yielded graphene with less polymeric residue after transfer than the use of poly­(methyl methacrylate) (PMMA) as the supporting layer. Hence, this dry and clean delamination technique for CVD graphene grown on copper substrates is highly advantageous for the cost-effective large-scale production of graphene, where the Cu substrate can be reused after each growth.

systems, they have numerous applications in various fields as pulsed power supply technology, [8,9] energy harvesting, [10][11][12] inverters, [13][14][15] and passive elements, [16][17][18] toward both defense and civil industries. Excellent energy storage capabilities of dielectric materials including high discharged energy density and high energy efficiency have long been eagerly pursued to meet the challenges and needs of the rapid development of modern industry, i.e., the low energy density of current dielectric materials results in overburdened capacitor volume and weight in electrical power systems. The energy storage performances of dielectric materials are usually multiply determined by three major electrical and dielectric parameters, which are categorized as:1) The breakdown strength E b ;2) The relative permittivity (also called dielectric constant) ε r or electric displacement D (the electric displacement is related to the polarization P by D = P + ε 0 E, here ε 0 = 8.85 × 10 −12 F m −1 is the vacuum permittivity); 3) The dielectric loss tanδ.In general, as illustrated in Figure 1, the discharged energy density of dielectric materials can be determined aswhere E is the applied electric field, and the energy efficiency is calculated by Dielectric polymer nanocomposites by integration of high-E b polymer matrix and high-D(ε r ) ceramic fillers have shown great potential for dielectric and energy storage applications in modern electronic and electrical systems. Interface between ceramic fillers and polymer matrix is considered as a predominant factor to determine the dielectric performances of the nanocomposites. This review analyzes the influence of the interface on dielectric responses and breakdown strength in the nanocomposites, and discusses the viability of current interface engineering strategies in improving their energy storage capabilities. Two scopes of current interface modification approaches are focused from both structural and functional considerations in the dielectric ceramics/polymer nanocomposites: first, the organic/inorganic interface compatibility can be modified to generate homogeneous dispersion of ceramic nanoparticles in polymer matrix, which is the premise of fully realizing the synergistic combination of advantages of polymer and ceramic fillers; second, regulated local electrical and dielectric behaviors in interface region enable the enhancement of dielectric properties (both high dielectric constant and high breakdown strength) in resultant nanocomposites. In the last part, some present challenges and future perspectives are proposed to utilize the interface strategy for developing high energy density ceramics/ polymer nanocomposites for dielectric and energy storage applications.

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High‐energy‐density polymer nanocomposites with high‐dielectric‐constant ceramic nanoparticles as the reinforcement exhibit great potential for energy storage applications in modern electronic and electrical systems. However, the decline of breakdown strength by high loading of ceramic nanoparticles hinders this composite approach from sustainable promotion of energy density. In this work, an approach is proposed and demonstrated by constructing gradient distribution of the spherical ceramic nanoparticles in the polymer matrix. These gradient‐structured nanocomposites possess remarkably improved mechanical and electrical behaviors, which give rise to ultrahigh breakdown strength and much‐promoted energy density. Moreover, this enhancement effect can be further enlarged via increasing the grades number of gradient structures. This work provides an effective strategy for developing flexible high‐energy‐density polymer/ceramic nanocomposites for dielectric and energy storage applications.

Dielectric polymer nanocomposites with high dielectric constant have wide applications in high energy density electronic devices. The introduction of high dielectric constant ceramic nanoparticles into a polymer represents an important route to fabricate nanocomposites with high dielectric constant. However, the nanocomposites prepared by this method generally suffer from relatively low breakdown strength and high dielectric loss, which limit the further increase of energy density and energy efficiency of the nanocomposites. In this contribution, by using core-satellite structured ultra-small silver (Ag) decorated barium titanate (BT) nanoassemblies, we successfully fabricated high dielectric constant polymer nanocomposites with enhanced breakdown strength and lower dielectric loss in comparison with conventional polymer-ceramic particulate nanocomposites. The discharged energy density and energy efficiency are derived from the dielectric displacement-electric field loops of the polymer nanocomposites. It is found that, by using the core-satellite structured Ag@BT nanoassemblies as fillers, the polymer nanocomposites can not only have higher discharged energy density but also have high energy efficiency. The mechanism behind the improved electrical properties was attributed to the Coulomb blockade effect and the quantum confinement effect of the introduced ultra-small Ag nanoparticles. This study could serve as an inspiration to enhance the energy storage densities of dielectric polymer nanocomposites.